Wire treating method



Oct. 10, 1944. w. l.. KEENE WIRE TREATING METHOD Filed Nov. 17. 1939 Patented Oct. 10, 1944 wma 'raEA'rmG METHOD Walter L. Keene, Dormont, Pa., assignorlto Bustless Iron and Steel Corporation, Baltimore, Md., a corporation of Delaware Application November 17, 1939, Serial No. 305,027

7 claims.

Myinvention relates to the treating of wire and the like for drawing purposes, and especially tothe annealing and subsequent lead-coating of wire or similar converted forms fashioned of the ferrous alloys, especially the stainless steel alloys. One objectof my invention isl the provision of a method and apparats forannealing and leading ferrous alloy wire in a simple, rapid, eilicient and thoroughly practical manner, correlating a desired annealing treatment of the wire with a thoroughly reliable leadingoperation giving a uniform and adherent coating to assure eiiicient drawing in a subsequent operation.

Another object is to produce a method of, and a unit for, continuously lead-coating wire formed of ferrous alloys,l characterized by the economy both in time, investment in equipment,`and costs of operation and maintenance, and in which the cost of supervision and labor is reduced to a minimum, all with the production of a uniform and adherent lead coatingcharacterized by the absence of sticking between adjacent strands of the leaded, Wire when the latter is reeled, by the absence of stretching or breaking when the leaded wire is unwound, and by the comparative readi- 'flux coating is applied and the ux loss is mainytained at a minimum, and which method is characterized by its. flexibility, and in which the equipment can be designed to handleany desired number of strands of wire.

Yet another object is to produce a composition for fluxingwires formed of ferrous alloys prior to lead-coating the same, characterized by its long useful life with a minimum of supervision and attention, and its low rate of consumption and low cost of operation.

Other objects and advantages in part will be obvious and in part pointed out hereinafter.;

My invention accordingly consists in the combination of elements, features of construction and arrangement of parts and in the'several operational steps, and in the relation of each of the same to one or more of the others, alias described herein, the scope of the application of which is indicated inthe claims at the end of the specification. A Y

For a more readycomprehension of my invention, reference may be had to the accompanying drawing, wherein, in schematic representation:

Figure l is a plan view of a continuous leadcoating unit according to my invention;

. Figure 2 is an elevation view of thelunit of Figure 1:

Figure 3 illustrates tails of the flux box which I prefer to employ in the unit of Figures 1 and 2;

While Figure 4 shows in fragmentary eleva- 1 tion certain details of a sinker roller in the lead pot of the unit of Figures 1 and 2.

Like reference characters denote like parts throughout the several views of the drawing.

As conducive to a more thorough understanding of my invention, I may point out at this time, that in the cold-drawing of stainless steel wires, certain diiiiculties are encountered. It is of course, to be understood that'the'term wire includes 'not only wire as conventionally known,

but also elongated solids of more important dimensions, such as rods, and in extreme cases,

even strip metal. I'hus wherever in the following specification and set of claims I employ the 'A term wire, it is used in its more comprehensive sense; Furthermore, whilejthe disclosure is directed particularly to the handling of chromiumcontaining stainless steels, it may also be employed advantageously in cold-drawing other ferrous alloys of considerable hardness and displaying a tendency towards embrittlement upon colddrawing. My invention accordingly is directed to the treatment of wires formed of such metals.

Stainless steel wire, even in the fully annealed condition, is considerably harder than annealed wire produced from ordinaryv carbon or low alloy steels. Also, stainless steel has the peculiar property of seizing upon or galling the die during the cold drawing operation with the result that drafts on uncoated wire are limited to small percentages of reduction in area if a satisfactory cold-drawn surface and economical die life are to be realized. In the case of the austenitic stainless steels which rapidly work-harden during the drawing opercepted practice consists in iirst annealing the l wire, then picltling the same to remove the scale,

in perspective certain dethrough the flux and then into the metal.

then lead-coating the wire, cold-drawing it until it becomes too hard or the lead coating too thin for satisfactory further reduction, then removproper gauge, it is simply annealed and pickled 'to give a scale-free, clean, white surface.

In the actual method of lead-coating, conventional practice has iecourse to a batch method of subjecting the wire to the lead bath. According to this customary practice, one or more coils of wireare dipped into a bath of molten lead, on the surface of which is carried an overlying layer o1' molten flux of special' composition. 'I'he coil of-'wire, as it is submerged in the bath, first passes By suspending the coil on a hook, it is possible to rotate it, both as it is lowered into the bath and while it is immersed therein, so that all surfaces of the metal come into contact, first with the flux, and then with the lead. When the operator is satisfied that the strands of the coil are properly leaded, the coil is raised from the bath, shaken as by twirling or thelike to remove the excess lead,`and water-quenched. The Wire is' operating conditions with the flux in good condition and the lead at proper temperatures-the lead coating obtained, while continuous and adherent where clean wire is treated, is lumpy and varies widely in thickness from say i000 of an inch to as-much as M of an inch or even more. This occasions increase in cost of lead, since such lumps represent outright' waste.

A further disadvantage of the batch process is that the lead coating on the several strands of wire which are wound in coils closely adjacent to each other tend to stick upon cooling from a molten condition. The water quench does not completely prevent this sticking. quently two or more turns of wire are secured together. Upon unwinding the wire,y the sticking together of the strands may cause the wire to stretch, or-even to break. This problem is particularly serious in the case of wires of small diameters, say 1A inch or less. Such a batch process requires careful supervision at all times by skilled labor.

In spite of the difficulties encountered in leadcoating by the batch process, the necessity of a suitable lubricant in cold-drawing stainless steels has caused recourse to some method of lead-coating to be practically invaluable in successful operation of a stainless steel wire mill. A considerable tonnage of stainless steel rods wound in coils, as well as the larger sizes of cold-drawn wire (annealed and pickled) is coated by this method.

ysulting from vcold-drawing the lead-coated wire.

A still further and very important object is to produce such a method of leadfcoating wire in which all possibility of the several turns of the coated wire sticking together is avoided.

In the process of coating such wires it is necessary first to flux the same, in-order to obtain an active or receptive surface, to which the lead v treatment it will not take up a coatingwhen it is dippedinto the molten lead unless it has thus been preliminarily fluxed.

In the batch process such as describedthe practicey has been to employ a flux consisting of a mixture of chlorides of zinc, ammonium and sodium. Such a. flux melts at about 650 F. I flnd this flux to be fairly satisfactory. In operation, however, this iux lcontinually loses ammonium chloride by volatilization, so that additions must be madefrom time to time. This flux is found to require constant s irring. For satisfactory operation, the flux mus be cleaned or skimmed off once a day, and replaced by a batch made up fresh. Additionally, difficulty is experienced 'in keeping the layer of iiux of sutilcient depth or thickness to ensure a complete and continuous coating. In short, while the use of such a iiuxing method is workable, it is found l to be wasteful and to require constant attention. The flux` is corrosive and tends to attack the pot,

resulting in increased maintenance costs. Even with careful supervision, it is found that probably because of the close proximityof the ad- Thus, frejacent turns of the coils of wire, the fiuxing frequently is spotty, resulting in unleaded spots on.

the coils. This necessitates a repetition of the uxing and leading step, with attendantappreciable increase in loss of time.

A further object of my invention is therefore, to produce a flux and method of iiuxing for use in preparing stainless steel wire for taking a lead coating, which is characterized by its small loss of material from vaporization or volatilization, which requires little if any agitation, which requires but little supervision, which can be readily maintained at properdepth o r thickness, which is economical and in the practice ofwhich a thin,

the several stations of the annealing and leadl several elements of the annealing and lead-coat- An object of my invention is to produce a conl tinuous method of lead-coating wires formed of stainless steels or other ferrous alloys, which is energy input required and of wear on dies recoating units, to take-up reels.. 'I'he speed at which the wire moves is so calculated, and the ing units are so dimensioned that the wire is retained at each station for thelength of time required to carry out each operation in a satisfactory manner. Extreme flexibility of the apparatus results' from the fact that within reason, any desired number of separate strands can be passed through the unit without contacting each other, all without materially increasing the volumetric dimensions of the unit and its several elements. This results in substantial economies, both in equipment and materials. Since the wire is unwound from separate take-oli reels, and is passed over separate guide sheaves to separate take-up sheaves, the several strands of wire come into contact with one another at no point during the process and are entirely independent of each other. In the following discussion I will limit my description to but a single strand of wire,

although it is to be understood that it is intended a suitable conduit I8.

that the method be applied to the simultaneous lead-coating of any desired number of strands Referring more particularly to Figure 1 of the drawing, a pluralityof like constructed take-oir reels 1 I0 are provided. Eight of these are illusl trated, indicating that this particular apparatus is adapted to handling eight strands of wire. It, of course, will be understood that it can be desired number of strands. In alignment with the take-off reels Iprovide guides II, I2. These guides may be of conventional type, and are shown as of suitable anti-friction construction, to facilitate passageof the wires therethrough.

To initiate operation, the wire is received from the wire mill, and if coated, this coating is removed by suitable pickling baths. The coils of wire are then placed on the take-off reels III.

vreadily adapted to the handling of any other As shown, vI prefer to dispose these reels IIl'vertica1ly,' although it is of course quite feasible to 'I3 is passed through one such alloy tube. Preferably, but a single strand I3 of wire is passed through any one alloy tube I1. However, it is .feasible to pass two or more Ystrands through feach tube if desired.

The temperature of the furnace, the rate of movement of the wire through the furnace, and

the length of the furnace are all so determined 40 that the wire is brought to a suitable annealing temperature while in the furnace. During its passage through the alloy tubes, the wire is 'ma/intained in a controlled ,atmosphere free from any traces of oxygen, water vapor, carbon dioxide, carbon monoxide, or other oxygen-containing gases. Preferably it is washed with a stream of mixed hydrogen and nitrogen gases resulting from the dissociation of anhydrous ammonia gas. This mixture of gases is introduced into alloy tube I'I from an ammonia dissociating unit generally indicated by the reference letter A, through The gases prevent any oxidation or discoloration of the surface of the wire during the annealing operation, thus preserving the original clean unoxidized metal surface. Contamination from the outside atmosphere is prevented'by assuring a ow of the mixedV gases outwardly through the tube entrances.v The gas preferably is burned at that point, thus giving visual indication of the outward flow.

Asia continuation of the annealing furnace, I preferably provide a cooling element `I9 through which vextend the tubes Il carrying the strands of wire I3. While this cooling element I9 may be of any suitable type now available, it preferably has a water-cooled cooling chamber 20 surrounding thetubesv II. .The element I9 is so dimensioned, and the initial temperature of any refrigerant which may be employed lis s'o selected, that by the time the wire I3 reaches the exit end of the furnace, it is cooled to room temperature.

I prefer to extend the tubes I1 to a sand box 2i shown partly in elevation and partly in section.

'I'his sand seal, in combination with the positive pressure of the gas, serves to prevent all ingress of air to the annealing furnace, thusguarding against oxidation of jthe wire therein. By the time the wire has passed through the sand seal it has cooled to a temperature at which there is no danger of significant oxidation upon exposure to air.

Upon passage from the sand seal, the wire is ready for fiuxing prior to being subjected t coating 'in the lead pot'.` Accordingly, the wire is passed 'through a ux box 22, shown in greater detail in Figure 2. 'Iheux box 22 contains a suitable flux, the surface of which is indicated at 23. A roller 24 is suitably mounted-as by trunnions, transversely of the box 22, and the wires'i3 are forced in anti-friction manner by said roller beneath the surface of the iiux. The flux is maintained at proper temperature by suitable heating means, as by steam exhausted through ports 2S of a steam pipe As previously indicated, the uxing operation must precede the lead-coating step for, although the metal is clean, bright and dry when it comes from the annealing furnace, a flux must be applied before thewi-re enters the molten lead. If the uxing step is omitted, 'the Wire will not take the lead coating.

Considering more particularly the fluxing step chlorides, either some or all, placed on top of the lead bath so that the wire would have to pass through the flux before it could reach the lead.

Although this technique proved moderately satisfactory, producing' a fairly good coating, it nevertheless possessed serious disadvantages. First of all, the corrosive action of the flux resulted in destruction of guide sheaves and the like. In addition, the iiux required constant stirring. Frequent additions oi ammoniuml chloride were required to replenish this ingredient which was lost by volatilization. Furthermore, itproved to be necessary, for consistently satisfactory re-v suits, to clean oi the spent iiux each day and to replace it with flux made up fresh. lSuch a requirement, of course, is undesirable in` a continuous method.

Moreover, dimculty was encountered in keeping l the flux of suiiicient depth to ensure complete and continuous covering of the metal witha coating of x. Thus, while the method was found to be workable, it required constant attention, and was wasteful of flux. Moreover, a difculty was encountered which also was present in the treatment of'coils in the batch process, namely that sometimes not all parts of the surface of the wire were uxed, so that these parts would not take leading was notfsofimportaht in the instance oi' batch processing, where it was a relatively simple matter to re-lead a spotty coil, this drawback `was serious in the case of my continuous process. Y

Here the wire must be properly coated in the rst place, because there is little possibility of repairing the coating at a later time.

I next conceived the idea,vwhich represents the I structural embodiment of the flux equipment of my present unit. of iiuxing the wire before passing it into the lead pot. To this end, I provide a. container consisting of a small, open-top box, on which I mount a. roller. The roller guides the wire through the ux, from whence guide sheaves conduct the wire to the lead pot proper, later to be described.

Before finally evolving the composition of flux which I now employ, I experimented with many types of fluxing agents. For example, I employed a flux consisting of a molten mixture of various combinations of zincl ammonium and sodium.

chlorides. This was substantially the flux commonly used in 'the known batch process. This ilux resulted in-a fairly good lead coating, and the corrosive action of the ux was fairly well confined to the flux box.` However,v the flux taken up froze to the wire and displayed a tendency to crack off before the wire passed under the surface ofthe lead in the lead pot. Thusy bare spots resultedv to which the lead failed to adhere. 'I'his, of course, results in an undesirable action during the subsequent cold-drawing operation. Additionally, flux losses were found to be excessively high..

' A second ux with which I experimented comprised concentrated hydrochloric acid and amaseaoos lture of 212'? F. than can be dissolved at 68 F. The addition of the hydrochloric acid apparently does not appreciably'aifect, this solubility of ammonium chloride in water.

Referring back to the operation of my lead coating process, the' bright annealed wire I3,

' emerging from the cooling chamber I9 of fur..

nace I4, passes through this ux 23, and picks up a coating of flux. While I am not certain of the exact action which the iiux has on the wire, anddesire not 'to' be bound by my proffered suggestion, I surmise that the acid presumably n further cleaning and activating the wire.

activates the surface of the Wire, and'as the wire emerges from the solution 23 it carries a thin film o f saturated ammonium chloride solution. Upon cooling. this solution throws oiI its excess ammonium chloride, most of the water evaporates, and the wire is then coated with a thin, uniform, adherent film of acidiiied ammonium chloride. The wire I3, bearing the iilm of ammonium chloride, is then carried into lead pot 2l.

When the wire with its coating of acidied ammonium chloride is carried under the molten lead, the ammonium chloride volatilizes, thus This cleaning action is probably what prevents the monium chloride. Here again, a fairly good lead coating was obtained, but the salt was observed to have a. tendency to settle out of the acid. At times, by consequence, the wire was found to pick up no lead inthe subsequent leading step. With the use of suitable mechanical agitators, however, I found this fluxing operation to be rather satisfactory.

As a further possibility, I had recourse to cold,

water solutions of ammonium and other chlorides either with or without additions of acid. 'These fluxes, either with or without additions of acid,- -were' found to be not particularly satisfactory,

because too much water was carried over into and under the lead, where it exerted an oxidizing action on the wire, and by virtue of the oxide coating produced kept the lead coating `from adhering to the wire. a l

Finally, I worked with a hot solution of wa- Yter, non-oxidizing acid, and ammonium chloride. This flux I found to give a completely satisfactory performance, the wire thus fiuxed taking a clean continuous. coating of lead. Working from this general combination", I evolved aflux which I now prefer to use in production work, comprising a` 10% tc'about 20% aqueous solution of hydrochloric acid saturated with ammo- While I have illustrated a manner and equipment for heating the. solution by the direct intro duction of steam, it will be understood that other heating methods may be employed, although where steam is directlyintroduced, I find that the water supplied by the steam just about com pensates for that lost through evaporation and that dragged out with the wire.

The eiiicacy of elevating. the temperature is strikingly emphasized by 'my experiments', whichv formation of an oxide film on the wire, which if present would prevent the lead from adhering.

Whilebest results are had with the flux thus described, in which the acid is in about the percentages noted, good resulilisfare achieved Where a high or lower acid 'content is used. For example, I have found that satisfactory results are realized where the percentage of acid is varied from about 5% to about 100%. In all cases, however, it is desirable to have the solution saturated'with ammonium chloride.

I havealso found that for best operation', the flux, regardless of percentage composition, at all times should be maintained at a temperature of at least about 2002F. The boiling point for such a flux is about 250 F. I have found operation at a iluxing temperature lower than 200 F, .to result in lead coatings l,which in the larger wire sizes are not completely satisfactory. By the use of such a temperature, I find that the wire carries over to the lead pot just the necessary quantity of flux. Satisfactory lead coatings are had and, moreover, the flux wastage is minimized.

While, of course, additions of both salt and on the part of the attendants vof the annealing' furnace is suiiicient for good results in the flux ing step, no direct labor is charged'against tnfluxing operation. The maintenance cost, therefore, is largely in the required heating and in salt and acid consumed.

, I find it advantageous to dump the flux and make it up anew after a longv shutdown of the unit, but one make-up will last about a weekor so under normal steady operating conditions. After that, the old flux should be dumped and a fresh batch made up. Y l

In the practiceof my process, I nd it sutilcient, for satisfactory fluxing, to pass the wire throughthe flux for an interval as short as one second. A good lead coating is obtainediwith the flux taken up. The usual variation of nuxing time is from about one second to about five seconds, although a greater length of -time is not show that over twice as much ammonium chloride can be dissolved in water at a temperaprejudicial. Apparently the time spent is sumcient t0 heat up the wire enough to aid in drying waste of material.

the ux retained as it leaves the flux bath. Moreover, the subsequent cooling of the wire and the adherent flux, apparently, tends to crystallize the ilux, possibly because of the lower solubility of the salt at the lower temperature. In any event,

. I iind that the time specified is suflicient to produce a satisfactory uniform adherent flux coating and a desired subsequent leadV coating.

' The flux composition which` I have described 'will prove satisfactory for the rapid and efficient iluxng of practically all grades of stainless steels with the exception of those of the 18-8 type l(18% chromium, 8% nickel) containing additions of molybdenum, columbium or titanium. I find,

- no doubt is due to the avidity with which this acid attacks the surface omdes and impurities, as well as the surface metal itself.

Continuing with the operational steps of my process, as the wire 3 travels from the flux box 22 to the lead pot 21 (Figures 1 and 3), it passes over sinker roller 28 (Figure 3). This comprises anl elongated rod 29, pivotally mounted at' its midpoint 30 on edge 3i of pot 27. The ends of rod 29 carry in suitable bearings, anti-friction rollers 32, 33. The wire i3 passes over the'topmost roller 32, and thence down and under the rollerv33,'being tensioned by take-up rollers, to be described. Roller 33 is xed in a position partially submerged in the molten lead 36. yThe moving wire is thus properly maintained in the lead bath in spite of the tension from the takeoff reels and the tendency to lift the roller 33 out of the lead. f

The Wire i3 thus picks up a coating of lead on its passage through the pot 21. This coating is continuous and adherent. The lead coating is found to be unusually smooth and even. This means good drawing in the dies. Moreover, it means a saving in lead, since lumps represent a In the leading step of my process, I find that a good working temperature is around '700 F, This temperature preferably should range from about 700 F. to about 900 F.

Depending upon the temperature of the lead. smooth coatings up to several thousandths of an inch are obtained. For example, with the lead at a temperature of 700 F2`0 F., the normal thickness of coating ranges from 2 to 4 thousandths of an inch.

It is sufficient, for a satisfactory leading operation, after proper fluxing, to pass the wire through the molten lead for a period of from about seconds to about 60 seconds, depending on the size'of the wire.

As a practical matter, I find it advantageous in operation according to my new invention, to keep. the surface of the molten metal 34 clean at the point of Ventry of the wire I3 thereinto. The rest of the surface of the lead preferably is covered with carbon to preventl loss of lead `thrmlghi oxidation by the atmosphere.

Following the passage of wire. I3 through lead pot 21, I pass theI coated wire through spray box 33. Here the wire is cooled by being subjected to a water spray. It then passes to variable speed take-up reels 36. The cooling station v35 is a very important element in the lead-coating ,i

unit, in that by cooling the coating to room temperature, I ensure that the lead is cold before the 9 strands of wire are wound into a coil on the takeup reels 36. In this way I ensure a freedom from adjacent strands of wire sticking together when coiled. xAs a consequence, the wire does not stretch or break when it is unwound. This is of particular value in the coating of the nner sizes of wire. It will be found that the wire as wound on takefup reels 36 is soft, clean, perfectly coated and ready for drawing.

' bright-annealing step, so that the operators han- 4'costs of this material per ton of wire.

\ culty is encountered in maintaining the temperature of the lead at a constant value, and the lead coating produced is foundto be smoother and more uniform'in thickness and the Wire consequently )is found to be easier to draw and, moreover, to present a more uniform drawn surface and be more uniform in gauge.

As many embodiments and variations may be made of my invention, and as changes may be v made in the embodiments hereinbefore set forth,

it will be understood that all matter described herein or shown in the accompanying drawing is tc be interpreted as illustrative, and not in a limiting sense.

I claimf' l. In the lead-coating of stainless steel wire, the art which comprises'the steps, in a continuous process, of passing the wire through a bright annealing furnace employing a dry atmosphere of hydrogen and nitrogen; thence Cinto a riuxing bath comprising anaqueous solution of hydrochloric acid and ammonium chloride, at a ternperature of about 200 to 250 F., to form, upon withdrawal into the `air a thin adherent coating of flux thereon; and thereafterv passing the wire through a bath of molten lead at a temperaturef'` ranging from about '700 F. to about 900 Li.

2. In the lead-coating vof stainless steel wire,

the art which comprises, in a process in which the wire is continuously passed through the several sequential steps of the process, the steps of passing the Wire through a bright annealing furnace employing a dry atmosphere of hydrogen and nitrogen, thence through a cooling 'chamber likewise having a dry atmosphere of nitrogen and hydrogen, then passing the wire through an aqueous flux solution comprising hydrochloric acid saturated with ammonium chloride and at a temperature of about 200 to 250 F., thence through air to permit evaporation ,of the solvent and deposit of an adherent flux coating, and thereafter passing the flux coated wirethrough a bath of molten lead maintained between 680 and 900 3. In the lead-coating of wiregformed of stainless steel, the art which comprises, in a process steps of passing the vwire through a heating chamber, thence through acooling chamber, both containing cracked anhydrous ammonia, then passing the wire through an aqueous iluir of hydrochloric acid saturated with ammonium chloride maintained at a temperature of 200 to 250 F. and thence into the air, and thereafter passing the wire through a bath of molten lead main- .tained between 680 to 900 F.

4. In the lead-coating of wire formed of stainless steel, the art which comprises, in a process in which the Wire is continuously passed through the several sequential steps of the process, the steps of passing the wire through a bright annealing furnace, thence through a cooling chamber, subjecting said wire while in said furnace and cooling chamber to an atmosphere of dry hydrogen-nitrogen gas, then passing` the wire through an aqueous ilux of hydrochloric acid saturated with ammonium chloride and maintained at a temperature of "200 to 250 F. and4 thenceout into the air to dry, thereafter passing the wire through 'a bath of molten lead maintained between 680 and 900 F., and then passing the wire through a cold water spray before reeling the same onto take-up reels.

5. In the lead-coating of stainless steel wire, ,the art which comprises the steps, in a continuous process, of passing the vwire through a bright annealing furnace employing adry atmosphere of hydrogen and nitrogen, thence into a ux `bath comprising an aqueous solution oi hydrochloric acid and ammonium chloride at a temperature of 200 to 250 F. in which any one part of the wire is subjected to said hot bath for a period of from about one second to about llve seconds, removing the wire from the bath to permit the ilux to dry thereon in the air, and thereaftervsub- Jecting the wire to a bath of molten llead maintained between 680 and 900 F. fora period of ten seconds to about sixty seconds.

6. In the lead-coating of stainless steel wire, the art which comprises, continuously passing the wire into a uxing bath comprising an aqueous solution of hydrochloric acid, hydroiluoric acid and ammonium chloride at a temperature oi' about 200 to 250 F; to form, upon withdrawal into the air, a thin, adherent coating of ux on the wire; and thereafter passing the wire through from about 700 F. to 900 F.

'7. In the lead-(coating of stainless steel wire containing one or more of molybdenum, columbium and titanium, the art which comprises, continuously passing the wire through a heating chamber, thence through a cooling chamber, both chambers containings a dry atmosphere of hydrogen and nitrogen, then passing the wire through an; aqueous uxing bath of hydrochloric acid and a bath of molten lead at a temperature ranging -hydrofluoric acid saturated with ammonium chloride and maintained at a temperature of about 200 to 250 F., and thence into the air to dry, and thereafter passing the wire through a bath of molten lead at a temperature of 680 to 900 F.

WAL'I'ER L. Kam. 

